1. Field of the Invention
This invention relates to a vehicle safety running control system, more particularly to a vehicle safety running control system which predicts or anticipates the possible decelerations of an obstacle present ahead of the vehicle to conduct contact avoidance control using the predicted decelerations.
2. Description of the Related Art
Various obstacle avoidance techniques have hitherto been proposed. For example, Japanese Laid-open Patent Application Hei 6(1994)-298022 teaches detecting the distance (relative distance) to an obstacle (e.g., another vehicle running ahead on the road) from the vehicle and automatically operating (i.e., independently of the vehicle operator's brake pedal manipulation) the braking system (and an alarm) so as to avoid contact with the obstacle.
In this prior art technique, the actual acceleration of the other vehicle (obstacle) is detected and, based on the detected acceleration, a first threshold value (relative distance) for avoiding the other vehicle by braking is determined. At the same time, a second threshold value (relative distance) for avoiding the obstacle by steering is determined based on the assumption that the subject vehicle moves to avoid the other vehicle with a lateral acceleration b0 after time .tau., measured from a certain point.
The system operates the braking system automatically only when the detected relative distance falls below the first and the second threshold values. Since the braking system is not operated at unexpected times which are not anticipated by the vehicle operator, the operator does not experience annoyance caused by operation of the automatic braking when he is intending to steer to avoid an obstacle, thereby improving the driving comfort and preventing annoyance of the vehicle operator.
In the prior art system, however, although the first threshold value is determined based on the acceleration in order that the braking system is not operated at times which are not expected or anticipated by the vehicle operator, the acceleration is that actually produced by the vehicle and is not a predicted or anticipated value.
The other vehicle running ahead on the road will behave in many ways, i.e., might accelerate to move away, might keep running at a constant speed, might decelerate suddenly to stop. The possible behavior of the other vehicle will thus have great or unlimited variance. If the obstacle avoidance control should be configured to cope with every possible behavior, the control will be extremely complicated. On the other hand, if the control should be configured in a standard or uniform fashion, its operation may sometimes not match with the driver's expectations.
Japanese Laid-open Patent Application Hei 5(1993)-181529 proposes predicting deceleration (predetermined deceleration) to use in the obstacle avoidance control. The deceleration predicted in the prior art is a single value and is only used to assist in the determination of whether obstacle avoidance operation should be effected. The prior art is thus not intended to cope with different decelerations possibly generated by the other vehicle.